The invention relates to an extension apparatus, especially for osteotomic surgery for the purpose of extending bones. This type of apparatus is also known as a "distraction device." However, in the following text, the apparatus will be referred to as an extending or extension means, which is employed for compensating differing lengths in the bone structure. Such differences in length may be in the nature of a birth defect or the result of an injury. Osteotomic surgery intends to correct such defects especially where the difference in length of limbs is substantial.
Devices of this type have the purpose to extend the two portions of a severed bone, which is fixed against lateral displacement in a continuous and/or in a stepwise manner. The extension must be such that during the entire treatment period the spacing between the severed bone portions is adjustable on the one hand with due regard to the desired lengthening and on the other hand, injury to the patient must be avoided.
Prior art devices for achieving the above purposes have been clinically tested. However, known devices and methods of the Anderson type require a prolonged bed confinement of the patient and thus involve all the disadvantages resulting from such confinement, for example, employing a so called Steinmann nail and a supracondyle extension bail for osteotomic extension purposes. A more recent method which has already been clinically tested is known as the Wagner extension osteotomy. According to this method the hollow bone is severed across its length. Two so called Schanz screws are inserted into the proximal and distal metaphyse in a percutaneous manner. The two bone portions are then slowly pulled apart with the aid of an extension apparatus. In the known Wagner method the patient himself may control the extension of the bone portions by means of a knurled handle forming part of the extension apparatus. The Wagner method does not require a prolonged immobilization of the patient who may leave the bed earlier than is required in case the supracondyle extension is employed. However, the Wagner method has the disadvantage that the Schanz screws require a percutaneous penetration or an open connection to the bone as well as the external attachment of the extension apparatus, whereby the danger of infection is increased. In addition, the chance of a mechanical fault or damage due to external influences such as impact, vibration, or the like is also increased. Besides, the Wagner apparatus is not quite suitable for the purpose of having the patient perform exercises. In other words, the patient may apply only a minimum load to the leg to which the apparatus is connected when the patient leaves the bed. However, it is well known that the healing process would be improved if the patient were able to move about in a less restrictive manner. Thus, even where the Wagner method is applied a prolonged hospitalization must be taken into account.